Reattachable introducer for a medical device deployment system

ABSTRACT

A reattachable introducer and method of using such introducer is disclosed for inserting an embolic coil deployment system into the tortuous vasculature of the human brain for placing an embolic coil within an aneurysm. The introducer includes a sheath having a lumen, a side opening and a longitudinal slit and includes a cylindrical sleeve slideably disposed about the sheath. A deployment catheter with a conical expander member is slideably disposed through the side opening of the sheath and through the lumen of the sheath. The conical expander member detaches the introducer from the deployment catheter through the longitudinal slit of the sheath, while the cylindrical sleeve reattaches the introducer to the deployment catheter through the longitudinal slit.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a reattachable introducer for inserting amedical device deployment system into the vasculature of a human bodyand further relates to a method of using such introducer. The deploymentsystem may be used for placing a medical device at a preselectedposition within a vessel. More particularly, the introducer is suitedfor inserting an embolic coil deployment system into the tortuousvasculature of the human brain for placing an embolic coil within ananeurysm.

2. Description of the Prior Art

For many years physicians have been placing various devices within ablood vessel of the human body in order to treat an aneurysm or toocclude a vessel. These devices are placed within the aneurysm or vesselusing one of several different catheter deployment systems. Thesedeployment systems transport and release the devices at a particularlocation within the vessel. The combination of different devices anddifferent deployment systems provide physicians with reliable methods oftreating aneurysms.

Physicians place various types of devices within an aneurysm or a vesselto occlude the flow of blood by promoting thrombus formation. Suchdevices include dilatation balloons, liquid medications, and emboliccoils. Embolic coils may take the form of helically wound coils,randomly wound coils, coils wound within other coils, and many othercoil configurations. These coils are generally formed of radiopaquemetallic materials, such as platinum, gold, and tungsten, or alloys ofthese metals. Often times, several coils are placed at a given locationin order to occlude the flow of blood through the vessel.

U.S. Pat. No. 6,179,857, entitled, “Stretch Resistant Embolic Coil WithVariable Stiffness” discloses one example of such an embolic coildesign. The coil disclosed in this patent is a helically wound coil, andvarious combinations of adjacent turns are spot welded together tocreate a stretch resistant coil of varying flexibility. U.S. Pat. No.6,183,491, entitled, “Embolic Coil Deployment System With ImprovedEmbolic Coil” discloses another embolic coil configuration which has arelatively flexible proximal portion which resists stretching.

Also, U.S. Pat. No. 5,853,418, entitled “Stretch ResistantVaso-occlusive Coils,” discloses a helically wound coil having apolymeric stretch resistant member extending through the lumen of thecoil and fixedly attached to both the distal end and the proximal end ofthe coil. Other examples of coil configurations are disclosed in U.S.Pat. No. 5,334,210, entitled, “Vascular Occlusion Assembly” and U.S.Pat. No. 5,382,259 entitled, “Vasoocclusion Coil With Attached TubularWoven Or Braided Fibrous Covering.” With all such coil designs, it isimportant that the coils remain very flexible so that they may be passedthrough vessels with the use of a catheter deployment system.

A variety of coil deployment systems are available for placing emboliccoils within an aneurysm or vessel. U.S. Pat. No. 6,113,622, entitled,“Embolic Coil Hydraulic Deployment System” and assigned to the sameassignee as the present patent application discloses one example of sucha deployment system. The hydraulic embolic coil deployment systemdisclosed in this patent uses fluid pressure which is applied to thelumen of the deployment catheter for expanding the distal sectionradially thereby releasing the embolic coil at a preselected position.

U.S. Pat. No. 5,350,397, entitled, “Axially Detachable Embolic CoilAssembly” discloses another known coil deployment system which utilizesa deployment catheter having a socket at the distal end for retaining aball which is bonded to the proximal end of the embolic coil. The ballis placed within the socket at the distal end of the deploymentcatheter, and the deployment system is then moved into a vessel to placethe coil at a desired position. A pusher wire with a piston at itsdistal end is pushed distally from the proximal end of the deploymentcatheter to thereby push the ball out of the socket and release the coilat the desired position.

Also, U.S. Pat. No. 5,263,964, entitled, “Coaxial Traction DetachmentApparatus and Method” discloses still another coil deployment system.The system disclosed in this patent uses glue or solder for attaching anembolic coil to a guidewire which is, in turn, pushed through a flexiblecatheter for positioning the coil within the vessel at a preselectedposition. Once the coil is at the desired position, the coil isrestrained by the deployment catheter, and the guidewire is pulled fromthe proximal end of the coil causing the coil to become detached fromthe guidewire and released from the deployment system.

Additionally, U.S. patent application Ser. No. 09/580,684 entitled,“Small Diameter Embolic Coil Hydraulic Deployment System,” filed on May30, 2000 and assigned to the same assignee as the present patentapplication, discloses a vasoocclusive coil deployment system forplacing a small diameter coil. In the system disclosed in this patent,the distal end of a cylindrical headpiece is inserted into and bonded tothe embolic coil. The proximal end of the cylindrical headpiece has adiameter approximately equal to the diameter of the lumen of adeployment catheter so that the cylindrical headpiece is disposed influid-tight engagement with the lumen of the deployment catheter. Whenfluid pressure is applied to the lumen of the deployment catheter, theouter wall of the distal section of the deployment catheter expandsradially and releases the cylindrical headpiece along with the emboliccoil.

Examples of other such coil deployment systems are disclosed in U.S.Pat. No. 5,122,136, entitled, “Endovascular Electrolytically DetachableGuidewire Tip For The Electroformation Of Thrombus In Arteries, Veins,Aneurysms, Vascular Malformations And Arteriovenous Fistulas” and U.S.Pat. No. 5,108,407, entitled, “Method And Apparatus For Placement Of AnEmbolic Coil.”

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention, there isprovided an embolic coil deployment system and reattachable introducertherefor which includes a sheath which takes the form of an elongatedflexible tubular member having a lumen extending therethrough and havinga proximal end, a distal end and an outer wall. The sheath has a sideopening in the outer wall of the sheath adjacent to the proximal end ofthe sheath. The sheath also has a longitudinal slit extending throughthe outer wall of the sheath and extending from the side opening and ina direction toward the distal end of the sheath. The reattachableintroducer also includes a cylindrical sleeve which is slideablydisposed about the sheath and is movable between the side opening of thesheath and the distal end of the sheath. Furthermore, the embolic coildeployment system includes a deployment catheter having a lumenextending therethrough and having a proximal section and a distalsection. The deployment catheter is slideably disposed through the sideopening of the sheath and through the lumen of the sheath. Finally, theembolic coil deployment system includes a vascular occlusive emboliccoil being detachably attached to the distal section of the deploymentcatheter.

In accordance with another aspect of the present invention, there isprovided a reattachable introducer for use with an embolic coildeployment catheter to place an embolic coil into an aneurysm. Theintroducer includes a sheath which takes the form of an elongatedflexible tubular member having a lumen extending therethrough and havinga proximal end, a distal end and an outer wall. The sheath has a sideopening in the outer wall of the sheath adjacent to the proximal end ofthe sheath. The sheath also has a longitudinal slit extending throughthe outer wall of the sheath and extending from said side opening towardthe distal end of the sheath. The introducer further includes acylindrical sleeve which is slideably disposed about the sheath and ismovable between the side opening of the sheath and the distal end of thesheath.

In accordance with still another aspect of the present invention, thereis provided a medical device deployment system and reattachableintroducer therefor which includes a sheath which takes the form of anelongated flexible tubular member having a lumen extending therethroughand having a proximal end, a distal end and an outer wall. The sheathhas a side opening in the outer wall of the sheath adjacent to proximalend of the sheath. The sheath also has a longitudinal slit extendingthrough the outer wall of the sheath and extending from the side openingand in a direction toward the distal end of the sheath. The reattachableintroducer also includes a cylindrical sleeve which is slideablydisposed about the sheath and is movable between the side opening of thesheath and the distal end of the sheath. Furthermore, the medical devicedeployment system includes a deployment catheter having a lumenextending therethrough and having a proximal section and a distalsection. The deployment catheter is slideably disposed through the sideopening of the sheath and through the lumen of the sheath. Finally, themedical device deployment system includes a medical device beingattached to the distal section of the deployment catheter.

In accordance with another aspect of the present invention, thedeployment catheter includes a conical expander member having a baseportion. The conical expander member tapers from the base portion toform a tip portion. The conical expander member is coaxially disposedabout the deployment catheter with the tip portion of the conicalexpander member extending distally from the base portion of the conicalexpander member so that as the deployment catheter is moved distally theexpander member causes the longitudinal slit to open thereby causing thesheath to separate from the deployment catheter.

In accordance with another aspect of the present invention, the sheathincludes a sheath stop which takes the form of a projection disposed onthe outer wall of the sheath at a position proximal to the distal end ofthe sheath.

In accordance with still another aspect of the present invention, thesheath includes a sheath stop which takes the form of a cylindrical ringhaving a lumen extending therethrough. The sheath stop is fixedlydisposed about the outer wall of the sheath at a position proximal tothe distal end of the sheath.

In accordance with yet another aspect of the present invention, thelongitudinal slit of the sheath extends from the side opening to thesheath stop, and the deployment catheter includes a winged hub attachedto the proximal section of the deployment catheter.

In accordance with another aspect of the present invention, the sideopening is generally circular and the side opening has a diametergreater than an outside diameter of the deployment catheter.

In accordance with still another aspect of the present invention, theside opening is generally oval in shape. The side opening has a majoraxis and a minor axis. The major axis of the side opening is generallyparallel with a longitudinal axis of the sheath. The minor axis of theside opening is generally greater than an outside diameter of thedeployment catheter.

In accordance with another aspect of the present invention, there isprovided a method for placing an embolic coil within an aneurysm or forplacing a medical device at a preselected position within a vessel. Themethod includes the step of providing a delivery catheter; areattachable introducer including a sheath having a lumen, a sideopening and a longitudinal slit; a cylindrical sleeve disposed about thesheath; a deployment catheter being slideably disposed through the sideopening of the sheath and through the lumen of the sheath; and avascular occlusive embolic coil or medical device being attached to thedistal section of the deployment catheter. The method also includes thestep of inserting the delivery catheter into the vasculature of the bodythen inserting the deployment catheter and introducer into a lumen ofthe delivery catheter.

Moreover, the method includes the step of sliding the cylindrical sleevedistally from the side opening of the sheath and toward the distal endof the sheath. The method also includes the step of pushing thedeployment catheter distally through the side opening causing the sheathto detach from the deployment catheter through the longitudinal slitthereby causing the embolic coil or medical device to become exposed.The method further includes the step of releasing the embolic coilwithin the aneurysm or the medical device at the preselected positionthen removing the deployment catheter and introducer. Finally, themethod includes the step of removing the delivery catheter from thebody.

In accordance with still another aspect of the present invention, thereis provided a method for retrieving a deployment catheter and an emboliccoil or medical device from the body. The method includes the step ofproviding a delivery catheter; a reattachable introducer including asheath having a lumen, a side opening and a longitudinal slit; acylindrical sleeve disposed about the sheath; a deployment catheterbeing slideably disposed through the side opening of the sheath andthrough the lumen of the sheath; and a vascular occlusive embolic coilor medical device being attached to the distal section of the deploymentcatheter. The method also includes the step of inserting the deliverycatheter into the vasculature of the body then inserting the deploymentcatheter and introducer into a lumen of the delivery catheter.

Moreover, the method includes the step of sliding the cylindrical sleevedistally from the side opening of the sheath and toward the distal endof the sheath. The method also includes the step of pushing thedeployment catheter distally through the side opening causing the sheathto detach from the deployment catheter through the longitudinal slitthereby causing the embolic coil or medical device to become exposed.The method further includes the step of pulling the deployment catheterproximally thereby causing the embolic coil or medical device to becomedisposed within the lumen of the sheath then sliding the cylindricalsleeve proximally toward the side opening of the sheath thereby causingthe sheath to reattach about the deployment catheter through thelongitudinal slit and causing the sheath to pinch the deploymentcatheter thereby preventing the sheath from sliding along the deploymentcatheter. Finally, the method includes the step of removing thedeployment catheter, introducer and delivery catheter from the body.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an enlarged perspective view of an embolic coil deploymentsystem with an introducer disposed about a deployment catheter;

FIG. 2 is an enlarged, sectional view of the introducer in accordancewith the present invention;

FIG. 2 a is an enlarged, cross-sectional view of the introducer of FIG.2 showing a longitudinal slit in an outer wall of the sheath;

FIG. 3 is an enlarged perspective view of the embolic coil deploymentsystem and introducer showing the deployment catheter being moveddistally, forcing the sheath off the deployment catheter and pushing anembolic coil out the end of the sheath; and,

FIG. 4 is an enlarged perspective view of the embolic coil deploymentsystem and introducer showing the deployment catheter and cylindricalsleeve being moved proximally thereby pulling the embolic coil back intothe sheath and forcing the sheath back onto the deployment catheter.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 illustrates a deployment catheter 12, a reattachable introducer14, and an embolic coil 16. The deployment catheter 12 is an elongatedtube with a lumen 18. Preferably, the proximal section 20 of thedeployment catheter 12 is formed of a polyurethane (Pellethane brand)material having a durometer in the range of about 60D to 75D. Theproximal section 20 is sufficiently flexible to traverse the vasculatureof the human body, but is sufficiently rigid so that it can be pusheddistally through the introducer 14. The distal section 22 of thedeployment catheter 12 is preferably formed of a polyurethane(Pellethane brand) material having a durometer of between 25D and 55Dwith a durometer of 40D being the preferred durometer.

The deployment catheter 12 also includes a winged hub 24 coupled to theproximal section 20 of the deployment catheter 12. The winged hub 24 maybe made from plastic and aids in the insertion of the deploymentcatheter 12 into the vasculature of the body. Furthermore, thedeployment catheter 12 includes a conical expander member 25. Theconical expander member 25 is coaxially disposed about the deploymentcatheter 12 and tapers from its base portion 25 a to its tip portion 25b. The tip portion 25 b of the conical expander member 25 is distal thebase portion 25 a. The conical expander member 25 is preferably madefrom the same material as the winged hub 24. Finally, the deploymentcatheter 12 includes an embolic coil 16 attached to the distal section22 of the deployment catheter 12. The embolic coil 16 may take variousforms and configurations and may even take the form of a randomly woundcoil, however, a helically wound flexible embolic coil is illustrated inFIG. 1.

FIG. 2 illustrates the introducer 14 which includes a sheath 26 which isapproximately 80 centimeters in length and is formed of a polymermaterial with a durometer in the range of about 50D and 80D. The sheath26 has a diameter of approximately 0.1 centimeters, and the lumen 28 ofthe sheath 26 has a diameter slightly greater than an outside diameterof the deployment catheter 12. The sheath 26 includes a side opening 30adjacent to the proximal end 32 of the sheath 26. The side opening 30 isa hole cut in the outer wall 34 of the sheath 26 and extends through theouter wall 34 and into the lumen 28 of the sheath 26. The side opening30 may take the form of a circle cut through the outer wall 34 of thesheath 26 or may take other configurations, like an oval. Preferably,the side opening 30 has a diameter in the range of about 0.23centimeters to 0.38 centimeters. The sheath 26 also includes alongitudinal slit 36 in the outer wall 34 of the sheath 26. Thelongitudinal slit 36 is approximately 60 centimeters in length andextends from the side opening 30 and in a direction toward the distalend 37 of the sheath 26.

The introducer 14 also includes a sheath stop 38 which is disposed aboutthe outer wall 34 of the sheath 26 at a position proximal to the distalend 37 of the sheath 26. The sheath stop 38 is cylindrical in shape andis made of nylon but may also be formed from plastic or a polymer. Thelength of the sheath stop 38 is approximately 1.3 centimeters while thepreferred diameter of the sheath stop 38 is 0.18 centimeters. Acylindrical sleeve 40 is slideably disposed about the sheath 26 and isapproximately 4.5 centimeters in length. The cylindrical sleeve 40 isgenerally cylindrical in shape and has a lumen 42. The cylindricalsleeve 40 is formed of polyethylene but may also be made from plastic ora polymer. The lumen 42 of the cylindrical sleeve 40 has a diameterslightly greater than the outside diameter of the sheath 26. Preferably,the outside diameter of the cylindrical sleeve 40 is 0.18 centimeters.

FIG. 2A illustrates a cross sectioned view of the sheath 26 between theside opening 30 and the cylindrical sleeve 40. The longitudinal slit 36runs through the outer wall 34 of the sheath 26 and into the lumen 28 ofthe sheath 26. The cylindrical sleeve 40 is slideably disposed about thesheath 26.

FIG. 3 illustrates the winged hub 24, conical expander member 25 anddeployment catheter 12 being moved distally through the side opening 30of the sheath 26, forcing the sheath 26 to separate from the deploymentcatheter 12 through the longitudinal slit 36 and pushing the emboliccoil 16 out the distal end 37 of the sheath 26.

FIG. 4 illustrates the winged hub 24, conical expander member 25 anddeployment catheter 12 being moved proximally, pulling the embolic coil16 back into the distal end 37 of the sheath 26. The cylindrical sleeve40 is moved proximally over the sheath 26 causing the sheath 26 toreattach about the deployment catheter 12 through the longitudinal slit36.

The introducer operates to place an embolic coil into an aneurysm of thebrain. With the introducer slideably disposed over a deploymentcatheter, the cylindrical sleeve is positioned generally over the sideopening causing the introducer to be pinched to the deployment catheter.In this configuration, the deployment catheter and introducer can beinserted into a delivery catheter (not shown), The sheath of theintroducer protects an embolic coil as the distal section of thedeployment catheter is inserted into the patient. The deploymentcatheter and introducer are inserted until the sheath stop generallyreaches the proximal end of the delivery catheter (not shown). At thispoint, the cylindrical sleeve is moved distally to expose said sideopening (FIG 3. Then, the deployment catheter is moved distally, causingthe conical expander member to move distally and forcing the sheath offthe deployment catheter (FIG 3. The sheath allows the deploymentcatheter to enter the vasculature more easily; otherwise, the flexibledeployment catheter would bend as it was being pushed distally. At thesame time the sheath is separating from the deployment catheter, theembolic coil attached to the distal section of the deployment catheterexits the sheath.

From this position, the physician can deploy the embolic coil at apreselected position within a vessel. Once the coil is no longerattached to the deployment catheter, the deployment catheter andintroducer are removed from the vasculature and another deploymentcatheter and introducer are introduced in the same manner when morecoils are required.

If, before the embolic coil is deployed, the physician decides toretrieve the coil, the sheath can be reattached, and the system can bereused. To do this, the deployment catheter is pulled proximally untilthe embolic coil is again disposed within the sheath. Then, thecylindrical sleeve is slid proximally (FIG. 4, reattaching the sheathonto the deployment catheter through the longitudinal slit. Thecylindrical sleeve is then slid generally over the side opening to holdthe sheath to the deployment catheter. Finally, the deployment catheterand introducer are removed from the patient.

A novel system has been disclosed in which an introducer is used tointroduce an embolic coil deployment system into the vasculature of thebody. Although a preferred embodiment of the invention has beendescribed, it is to be understood that various modifications may be madeby those skilled in the art without departing from the scope of thepresent invention. For example, there are many variations andmodifications of the embolic coil, including numerous coil windingconfigurations, or alternatively, other types of vascular occlusivedevices may be utilized, such as dilation balloons, radiopaque fluids,and liquid medications.

These and other modifications would be apparent to those having ordinaryskill in the art to which this invention relates and are intended to bewithin the scope of the claims which follow.

1. A method for placing an embolic coil within an aneurysm, said methodcomprising the steps of: providing a delivery catheter; a reattachableintroducer including a sheath having a lumen, a side opening through theouter wall of said sheath and a longitudinal slit, and including acylindrical sleeve slideably disposed about said sheath; a deploymentcatheter being slideably disposed through the side opening of saidsheath and through the lumen of said sheath; and a vascular occlusiveembolic coil being detachably attached to a distal section of saiddeployment catheter; inserting said delivery catheter into a vessel ofthe body; inserting said deployment catheter and said introducer into alumen of said delivery catheter; sliding said cylindrical sleevedistally from a position adjacent to said side opening through the outerwall of said sheath and toward the distal end of said sheath; advancingsaid deployment catheter distally while causing said sheath to partiallydetach from said deployment catheter by extending through saidlongitudinal slit, thereby causing said embolic coil to become exposed;releasing said embolic coil within the aneurysm; removing saiddeployment catheter and said introducer; and removing said deliverycatheter from the body.
 2. A method for retrieving a deployment catheterand an embolic coil from the body, said method comprising the steps of:providing a delivery catheter; a reattachable introducer including asheath having a lumen, a side opening through the outer wall of saidsheath and a longitudinal slit, and including a cylindrical sleeveslideably disposed about said sheath; a deployment catheter beingslideably disposed through the side opening of said sheath and throughthe lumen of said sheath; and a vascular occlusive embolic coil beingdetachably attached to a distal section of said deployment catheter;inserting said delivery catheter into a vessel of the body; insertingsaid deployment catheter and said introducer into a lumen of saiddelivery catheter; sliding said cylindrical sleeve distally from aposition adjacent to said side opening through the outer wall of saidsheath and toward the distal end of said sheath; advancing saiddeployment catheter distally while causing said sheath to partiallydetach from said deployment catheter by extending through saidlongitudinal slit thereby causing said embolic coil to become exposed;pulling said deployment catheter proximally thereby causing said emboliccoil to become disposed again within the lumen of said sheath; slidingsaid sleeve proximally toward the side opening of said sheath therebycausing said sheath to reattach into said deployment catheter throughsaid longitudinal slit and causing said sheath to pinch said deploymentcatheter adjacent to said side opening through the outer wall of thesheath, thereby preventing said sheath from sliding along saiddeployment catheter; removing said deployment catheter and saidintroducer; and removing said delivery catheter from the body.
 3. Amethod for placing a medical device at a preselected position within avessel, said method comprising the steps of: providing a deliverycatheter; a reattachable introducer including a sheath having a lumen, aside opening cut through the outer wall of said sheath and alongitudinal slit and including a cylindrical sleeve slideably disposedabout said sheath; a deployment catheter being slideably disposedthrough the side opening of said sheath and through the lumen of saidsheath; and a medical device being detachably attached to a distalsection of said deployment catheter; inserting said delivery catheterinto a vessel of the body; inserting said deployment catheter and saidintroducer into a lumen of said delivery catheter; sliding saidcylindrical sleeve distally from said side opening through the outerwall of said sheath and toward the distal end of said sheath; pushingsaid deployment catheter distally through said side opening through theouter wall causing said sheath to detach from said deployment catheterthrough said longitudinally slit thereby causing said embolic coil tobecome exposed; releasing said medical device at the preselectedposition within the vessel; removing said deployment catheter and saidintroducer; and removing said delivery catheter from the body.
 4. Themethod of claim 3 in which, prior to sliding said cylindrical sleevedistally from said side opening through the outer wall of the sheath,the cylindrical sleeve causes the sheath to pinch the deploymentcatheter, thereby preventing the sheath from sliding along thedeployment catheter.
 5. A method for retrieving a deployment catheterand a medical device from the body!said method comprising the steps of:providing a delivery catheter; a reattachable introducer including asheath having a lumen, a side opening cut through the outer wall of saidsheath and a longitudinal slit and including a cylindrical sleeveslideably disposed about said sheath; a deployment catheter beingslideably disposed through the side opening of said sheath and throughthe lumen of said sheath; and a medical device being detachably attachedto a distal section of said deployment catheter; inserting said deliverycatheter into a vessel of the body; inserting said deployment catheterand said introducer into a lumen of said delivery catheter; sliding saidcylindrical sleeve distally from said side opening through the outerwall of said sheath and toward the distal end of said sheath; pushingsaid deployment catheter distally through said side opening through theouter wall of the sheath causing said sheath to detach from saiddeployment catheter through said longitudinal slit thereby causing saidmedical device to become exposed; pulling said deployment catheterproximally thereby causing said medical device to become disposed withinthe lumen of said sheath; sliding said sleeve proximally toward the sideopening through the outer wall of said sheath thereby causing saidsheath to reattach about said deployment catheter through saidlongitudinal slit and causing said sheath to pinch said deploymentcatheter thereby preventing said sheath from sliding along saiddeployment catheter; removing said deployment catheter and saidintroducer; and removing said delivery catheter from the body.
 6. Themethod of claim 5 in which, prior to sliding said cylindrical sleevedistally from said side opening through the outer wall of the sheath,the cylindrical sleeve causes the sheath to pinch the deploymentcatheter, thereby preventing the sheath from sliding along thedeployment catheter.